Power assist steering systems are well known in the art. They are frequently employed for use with automotive vehicles. The power assist is accomplished by applying a supplementary rotary force to a steering member. Such systems may be controlled in response to a driver's applied torque to the vehicle's steering wheels. Some of the systems provide steering assist by using hydraulic power and others by using electric power.
U.S. Pat. No. 4,660,671 discloses a DC electric assist motor. The motor includes a rotatable armature encircling a steering member which has a thread convolution portion thereon and a portion having a rack thereon. Rotation of the electric assist motor armature causes linear movement of the steering wheel through a ball-nut drive arrangement in combination with the thread convolution portion of the steering member. A torque sensing means is coupled to the steering column to sense driver applied input torque to the steering wheel. The torque sensing device uses a magnetic Hall-effect sensor arrangement for sensing relative rotation between the input and output shafts across a torsion bar. An electric control circuit monitors the signal from the torque sensing means and controls the electric assist motor in response thereto.
U.S. Pat. No. 4,682,104 discloses an angular displacement sensor for use in detecting applied steering torque between an input shaft and an output shaft wherein the shafts are coaxially aligned with each other and rotatable relative to each other about a common axis. The sensor includes an input rotary transformer which includes a stationary primary winding and a rotary secondary winding. The secondary winding is mounted on one face of an annular disc which is, in turn, mounted on the input shaft for rotation therewith. Axially displaced from the input rotary transformer there is provided a pair of detection disks including a transmitter disk and a receiver disk. The opposing faces of these disks carry identical planar coils with the coils being in the shape of spirally wound sectors coiled alternately in opposing directions and coaxially surrounding the common axis of the input and output shafts. An AC voltage applied to the primary of the input rotary transformer is applied to the planar coils on the transmitter disk. This causes a voltage to be induced in the planar coils mounted on the receiver disk. A single output planar rotary transformer is employed having a primary winding mounted on a disk and coaxially surrounding the output shaft. The output transformer also includes a single stationary secondary winding on another disk axially spaced from the primary winding of the output transformer. A single output signal is provided which varies with angular deviation between the input and output shafts.